1. Field of the Invention
The present invention refers to a yarn storage and feed device.
2. Description of Prior Art
In the case of known yarn storage and feed devices, the stopping element is arranged at a comparatively large axial distance from the last winding of the yarn supply close to the head of the storage member. The position of the stopping element is chosen with due regard to the fact that all imaginable yarn qualities are to be processed by the yarn storage and feed device and that, when using the same length in the yarn supply for essentially all the yarn qualities, a substantial axial distance between the last winding in the yarn supply and the stopping element and a comparatively large angle between the last winding in the yarn supply and the yarn section moving from the last yarn winding to the stopping element still exist even in the case of the coarsest yarn. Especially when multicolor weaving is performed on a jet weaving machine, a group of such yarn storage and feed devices is provided, only one of said devices being in operation, whereas the others are at rest. However, the yarns of the yarn storage and feed devices which are at rest always extend up to and into the main nozzle of the weaving machine where they are permanently acted upon by a pressure medium flow and thus kept at hand for the next insertion process. In view of the fact that the main nozzle and the reed oscillate and the yarn is acted upon by the standby pulling force, at least the last winding will be axially opened in a manner comparable to a helical spring having a pulling force applied thereto, this being due to the large angle between the last winding and the yarn section extending towards the stopping element. This will cause an increase in the length of the yarn downstream of the stopping element so that the free end of the yarn moves out of the main nozzle. The cutting device, which is associated with the main nozzle and provided for all yarns and which is periodically actuated for the color which is just being processed, cuts off this increase in length. The resultant yarn pieces will not only cause uncontrollable interfering effects in this critical operating area but they will also penetrate into the woven fabric and deteriorate its quality.
It is true that, in the case of a yarn storage and feed device comprising several stopping elements which are distributed around the circumference of the storage member in spaced relationship with one another (EP 264985), it is known to axially displace the stopping elements during the yarn withdrawl and insertion process so as to be able to determine--in spite of the spaces between the individual stopping elements--precisely, without any discontinuity, the length of yarn to be inserted. This principle, however, does not take into account the processes taking place in the yarn supply in the period of rest and it cannot provide any suggestions with regard to the solution of the problem described at the beginning.
FIG. 1 and 2 disclose a yarn storage and feed device 1' having a known structural design, in the case of which components which are of secondary importance in understanding the function have been omitted. Such yarn storage and feed devices 1' are often used for multicolor weaving on jet weaving machines W so as to supply to the jet weaving machine W weft yarn sections of a precise length, said weft yarn sections being drawn off a supply bobbin (not shown) as a continuous yarn F. The exact dimensioning of every weft yarn section is effected with the aid of a means, which is not shown and which is incorporated into the yarn storage and feed device 1', said means including either, in the case of a cylindrical storage member 2 having an adjustable outer diameter, a single stopping element 13, which interrupts the yarn take-off process when a predetermined yarn length has been reached, or, in the case of a storage member having a fixed outer diameter, several stopping elements 13, which are distributed over the circumference of said storage member at regular intervals and which are used for interrupting the yarn take-off process at a respective stopping element 13 which has been selected. This principle is, however, known so that there is no need of discussing it in the present connection.
In addition to the e.g. non-rotatably fixed storage member 2, which defines a storage surface 4 and the axis of which is provided with reference numeral 3, the yarn storage and feed device 1' is equipped with a winding element 5 which is adapted to be caused to rotate by means of a drive motor 6. The winding element 5 is hollow so that the yarn F coming from the bobbin is guided in the interior of said element along the axis 3 and then radially outwards to a location where it is spirally wound onto the storage surface 4 in successive windings 11 in a yarn supply S. The drive motor 6 is connected to a control device 7, which is, in turn, connected to a maximum sensor 8 and a minimum sensor 9 through a control line 10. If desired, the minimum sensor 9 can also be omitted. The two sensors 8, 9 are responsible for actuating and deactuating the drive motor 6 in such a way that, when the size of the yarn supply S falls below a specific limit, the drive motor 6 will be energized unitl the maximum sensor 8 detects the necessary size of the yarn supply S and deenergizes the drive motor 6.
In the yarn supply S, the individual windings 11 are positioned side by side. The last winding 11' faces the stopping element 13, which is located at a comparatively large axial distance A from the yarn supply S.
The stopping element 13 is adapted to be moved between a passive position, in which the yarn F can be unwound unhindered and with a circulating movement around the storage surface 4 and its head, and a stopping position (FIG. 1 and 2), in which the yarn is prevented from carrying out the circulating take-off movement and is deflected via the stopping element 13. On its path leading to the weaving machine W, the yarn F is then redeflected towards the axis 3 via the head of the storage member 2 prior to running through a yarn eye 14 and from said yarn eye into a passage 15a of a main nozzle 15 of the weaving machine W. The main nozzle 15, which is connected to a pressure medium supply, is attached to the reed (not shown) at the inlet to the shed in such a way that it will be oscillatingly moved together with the reed in the course of the reciprocating movement of said reed (double arrow 17). The main nozzle 15 includes a number of passages corresponding to the number of colors which are being processed; in the present case, it includes the passage 15a for the yarn F and a passage 15b for a second yarn F" which is just being processed and which comes from a yarn eye 16.
In the case of multicolor weaving, the weaving machine W has associated therewith a number of yarn storage and supply devices 1' corresponding to the number of colors. The yarn storage and feed device 1' with the color (yarn F) which is not being processed at the moment is at rest (FIG. 1 and 2). During the period of rest, the passage 15a is acted upon by a pressure medium flow, which applies to the yarn F a permanent standby pulling force P (i.e. take-off tension) in the direction of the shed and which keeps said yarn F straight. The free end F' of the yarn F projects beyond the main nozzle up to and into the area of a cutting device 18, which is common to all yarns processed and which, when the reed is moving, is periodically actuated, e.g. for the purpose of cutting the yarn F". The free end F' of the yarn F projects beyond the main nozzle 15 by a length L.
FIG. 1 shows the commencement of the period of rest of the device 1'. The other yarn F" is just being inserted. The section 12 of the yarn F and the last winding 11', which is located directly adjacent the windings 11 in the yarn supply S, include an angle .alpha.. The standby pulling force P is permanently effective.
Due to the standby pulling force P and due to the oscillating movement (double arrow 17) of the main nozzle 15, an axially directed force component resulting from the standby pulling force and its oscillation becomes effective in the yarn F, said force component starting to gradually open--according to FIG. 2--at least the last winding 11', similar to a helical spring having an axial tension load applied thereto. The major part of at least the last winding 11' starts to migrate gradually towards the stopping element 13. Due to this migrating movement and in view of the fact that the bend between the section 12 and the last winding 11' stretches and forms an (in the layout of the storage surface 4) essentially straight line, the free end F' of the yarn F will migrate further out of the main nozzle 15 and into the shed, the distance along which said migration takes place being the distance L1. This increase in length will, however, have the effect that in the case of the next actuation of the cutting device 18 for the purpose of cutting to length a section of the yarn F" which is just being processed, a piece x of the yarn F will be cut off which will drop freely or which will be carried into the shed. These free yarn pieces x arise from each yarn during the period of rest and this will progressively result in a strong contamination of the insertion inlet and in uncontrollable faults of the woven fabric.